Some 450 million years ago, plants first spread out over the land. As slow colonization progressed, an interaction began between the underlying rock and the remains of plants. Soil, in all its various forms, was gradually being produced and eventually became the land form upon which all life on Earth ultimately depends.
The ability of animals to move allows them freedom to choose favorable habitats, even under changing conditions. A plant, on the other hand, is usually in one place for life, its root system hidden, and its destiny dependent on the soil for anchorage, nutrients and moisture.

Plants are highly resilient and can survive in very marginal conditions, actually growing out of rock and even brickwork, and they are certainly capable of living in very poor soil. Many plants grow on other plants. These are known as epiphytes and are usually found high up in trees in tropical rain forests.

The important thing to remember about your own garden is that you are pretty much stuck with whatever you have in the way of garden soil. You cannot completely dig it out and replace it, so you must get to know it, if you are to cultivate it successfully. You need to understand its texture and whether it consists of heavy clay or light, sandy soil. You need to find out its pH in order to ascertain how acidic or how alkaline it is. Then you are in a position to choose the plant material that is most suited to that environment.

Different kinds of soil are found in different regions of the world. The ground-down particles of rock form the underlying basis of the soil—sand, silt, clay or loam, the most ideal—to which organic elements are added from the decomposed remains of plants and animals.

In a country like the United States, which has been cultivated for hundreds of years, the soil is made up of not only the underlying geological strata, but also of the products of years of farming. As a result, the soils are many and varied. Clays, sands, and loams all give color and texture to the patchwork of fields once typical of the countryside.

Deep, dark, rich soils are particularly good at supporting crops such as vegetables and grasses. The dead organic remains from previous crops retain moisture, feed biological life and ensure good soil structure. Other edible crops prefer lighter, more free-draining soils with rather higher levels of mineral nutrients. The good news is that you can always improve the structure of your soil by amending it with the appropriate materials to achieve the desired structure for the plants you are growing.

In our gardens, soils are even more varied than those under the plow. Most of them are able to support a colorful range of handsome plants. Even those from the most remote or exotic parts of the world seem to find an agreeable climate somewhere in our gardens. However, in order to grow a wide range of healthy plants, you need to know what your soil is composed of, and if necessary, how to improve it.